The present invention relates to a method and apparatus of optometry.
In the conventional method and apparatus of optometry, a split target having a special shape (e.g., slit shape) is projected on to the fundus of a subject and the refractive power of the subjects eye is measured based on the split value. This method is called "objective optometry". Alternatively, a person being tested under test) is requested to observe an optometrical target such as a landolt's ring through a correcting optical system, which is adjusted until the person is able to clearly see the target. The refractive power is indicated by the amount of adjustment. This method is known as "subjective optometry".
The method and apparatus of objective optometry is advantageous in that a person under test does not need to make a response, while the apparatus of subjective optometry is superior in connection with determining optimal correcting power for the subject. In this connection, a method adopted recently involves a) using an objective optometry apparatus to measure the approximate correcting power, thus obviating the awkwardness involved with having a person respond during testing the resulting inaccuracy of measurement; and thereafter b) using a separate or built-in subjective optometry apparatus to determine the final correcting power based on measurements using objective optometry.
There has been proposed a subjective optometry apparatus in which a target image on the fundus of a subject is formed on an imaging device and the target image signal is multiplied by a signal response function after the retina so that the inspector can view the same target image as that the person under test is observing. Refer to Japanese Patent Publication No. 4-17047.
For more accurate measurement by eliminating an erroneous response made by a person under test, it is desirable for the above-mentioned subjective optometry apparatus to enable the inspector to view the state of observation of the person, however, this is not feasible with the conventional apparatus.
Even if it is intended to let a person under test observe a target for subjective optometry and to view the target image formed on the fundus of the subject by means of a general imaging device, it is difficult to get a clear target image due to a low reflectivity of the fundus and a low sensitivity of the imaging device.